Optical discs have become popular storage media nowadays. An optical storage apparatus, such as an optical disc drive, is therefore equipped with the data recording capability to record user data onto an optical storage medium, such as an optical disc. In general, a laser diode driver (LDD) is electrically connected between a controller and a laser diode for receiving driving and control signals generated from the controller to drive a laser diode (LD) to emit a laser beam with a designated laser power for data recording. FIG. 1 is a block diagram illustrating a conventional laser diode driving system 100. As one can see, the exemplary LDD 104 includes a plurality of current amplifiers 112_1, 112_2, 112_3 and a plurality of switches 114_1, 114_2, 114_3. The controller 102 outputs driving currents IIN1, IIN2, IIN3 to the current amplifiers 112_1, 112_2, 112_3, respectively; in addition, the controller 102 generates write enable signals WEN1, WEN2, WEN3 to the LDD 104 to serve as output enable signals OE1, OE2, OE3 which control on/off states of the respective switches 114_1, 114_2, 114_3. With proper control of the switches 114_1, 114_2, 114_3, the amplified currents generated from the current amplifiers 112_1, 112_2, 112_3 are selectively combined at the output node N to drive the following LD 106 to emit a laser beam with a specific laser power P which is in proportion to the LD driving current received from the output node N.
Please refer to FIG. 2, which is a waveform diagram illustrating the laser power P (or the LD driving current) and the write enable signals WEN1, WEN2, WEN3. Taking a Blu-ray disc (BD) for example, the adopted write strategy supports power shape types including a block type, an L-shape type and a castle type. As shown in FIG. 2, the power symbols include a cooling power Pc, a space power Ps, a write power Pw, and a middle power Pm. For clarity and simplicity, each power symbol (power level) has duration equal to 1T (i.e., one power symbol period is 1T). Regarding the conventional write pulse transmission design, a minimum transmission pulse width equal to 1T may occur. For example, to produce the desired power shape type (i.e., block type, L-shape type or castle type), the length of the high transmission pulse of the write enable signal WEN2 between T1 and T2 is required to be 1T; regarding the write enable signal WEN1, the length of one low transmission pulse between T2 and T3, the length of another low transmission pulse between T6 and T7, and the length of yet another low transmission pulse between T11 and T12 are required to be 1T; additionally, regarding the write enable signal WEN3, the length of a first high transmission pulse between T1 and T2, the length of a second high transmission pulse between T4 and T5, the length of a third high transmission pulse between T8 and T9, and the length of a fourth high transmission pulse between T10 and T11 are required to be 1T. As the controller 102 is generally an unmovable control chip disposed in the optical storage apparatus, and the LDD 104 and LD 106 are disposed on a movable optical pick-up head of the optical storage apparatus, a flex cable is therefore used to electrically connect the controller 102 to the LDD 104. However, in a case where the high-speed data recording is enabled, the transmission period of 1T may be 1.26 ns or less, which is shorter than the flex cable's minimum transmission pulse period, say, 2 ns. Therefore, the effective bandwidth of the flex cable fails to meet the requirements for transmitting 1T short transmission pulses generated under the high-speed data recording operation, leading to poor signal transmission quality between the controller 102 and the LDD 104. As a result, the write quality is significantly degraded because the switches 114_1, 114_2, 114_3 cannot be accurately controlled to make the LD 106 produce laser pulses with the desired power shape.
Due to factors deteriorating the transmission quality including the impedance discontinuity and the signal loss and crosstalk of the flex cable connected between the controller and the LDD, it is better to avoid the delivery of any short transmission pulses (e.g., 1T transmission pulses) from the controller to the LDD. Therefore, an innovative scheme of transmitting the control signals, such as the write enable signals, via the flex cable connected between the controller and the LDD is needed.